1. Field of the Invention
This invention relates to a heat method and apparatus for separting sections of a covering on an article, and more particularly to a heat method and apparatus for desheathing thermoplastic jacketed cable having an irregular periphery.
2. Description of the Prior Art
A common method of desheathing the leading end portion of a thermoplastic jacketed cable involves making a circumferential cut in the jacket of the cable adjacent its leading end with a hand-held knife or other type of hand-held cutting tool, and then manually pulling the jacket leading end portion from the cable. This method is undesirable because the operator may cut through the jacket and into the insulation on the conductor wires of the cable, and in certain instances, actually nick the wires, producing defects in the cable whereby it develops shorted or open conductors in use.
The foregoing is true even in instances where the desheathing tool is of a type in which a cutting blade can be preset to produce a depth of cut corresponding to the nominal jacket thickness, because of variations in the thickness of the cable jacket. Specifically, if a cut is being made in a place where the jacket is relatively thin, the blade may cut too deep and nick the insulation on the cable conductors. In other instances, where the jacket is relatively thick, the blade will not cut deep enough to allow jacket separation without tearing of the jacket. Further, where the cable has an irregular periphery, such as in vinyl plastic jacketed cable used in PBX and telephone switching equipment, the operator must use extreme care in order to consistently make a clean uniform cut through the cable jacket around its entire periphery without damaging the insulation on the conductors.
The use of heated cable desheathing cutting blades which come into actual contact with the cable jacket to facilitate separation thereof also is known, but is undesirable for various reasons. For example, in instances where the jacket of the cable is relatively thin the heated cutting blades can pass through the jacket and damage the insulation on the cable conductors. The plastic jacket of the cable also tends to stick to the heated blades, requiring frequent cleaning thereof. Further, the heated cutting blades provide no particular advantage over an unheated blade from the standpoint of achieving a clean uniform cut about a cable having an irregular periphery.
U.S. Pat. No. 3,659,332, issued May 2, 1972 to R. F. Morrone, discloses the removal of insulation from leading end portions of the conductors of a flat cable by utilizing infrared heat to vaporize insulation on a portion of the cable spaced from the leading end thereof along a desired line of separation. Application of heat then is terminated to permit any remaining insulation in the heat zone to cool so that it will fracture when placed in tension, after which the leading end portions of the insulation are pulled from the conductors.
Also of interest to this invention is the U.S. Pat. No. 2,432,868, issued Dec. 16, 1947 to J. A. Earl et al, which is directed to the burning of insulation off of a leading end portion of a wire, and the U.S. Pat. No. 2,636,408, issued Apr. 28, 1953 to W. T. Mitchell, in which insulation on a wire is heated with high frequency electromagnetic energy to facilitate subsequent stripping of the insulation from the wire in a separate stripping device.